Sensorineural type of hearing loss is due to the absence or the destruction of the hair cells in the cochlea, which are needed to convert acoustic signals into auditory nerve impulses. People suffering from such type of loss are unable to derive any benefit from conventional hearing aid systems. This is because their mechanism for converting sound energy into auditory nerve impulses has been damaged or substantially damaged.
To overcome sensorineural deafness, numerous Implantable Cochlear Stimulation (ICS) systems—or cochlear prosthesis/implant—have been developed which seek to bypass the hair cells in the cochlea by presenting electrical stimuli directly to the auditory nerve fibers, leading to the perception of sound in the brain and at least a partial restoration of hearing function. The common denominators in most of these cochlear implants have been the implantation of electrodes into the cochlea, and a suitable external source of an electrical signal for the electrodes.
In order to effectively stimulate the nerve cells, the electronic circuitry and the electrode array of the cochlear prosthesis perform the function of separating the acoustic signal into a number of channels of information, each representing the intensity of a narrow frequency range within the acoustic spectrum. Ideally, the electrode array would convey each channel of information selectively to the subset of auditory nerve cells. The nerve cells are arranged in an orderly tonotopic sequence, from high frequencies at the basal end of the cochlear spiral to progressively lower frequencies towards the apex, and ideally the entire length of the cochlea would be stimulated by electrode array implanted in the cochlea to provide a full or substantially full frequency range of hearing.
The signal provided to the electrode array is generated by a signal processing component of the Implantable Cochlear Stimulation (ICS) system. An incoming acoustic signal is processed by a family of bandpass filters. Then, the output of each bandpass filter is independently amplitude mapped into a simulation level, using a mapping consistent with normal perception. However, conventional techniques do not provide for an adaptive mapping.
There is a need to offer an improved experience to a cochlear implant user by utilizing a mapping technique that automatically adapts in accordance with the environment of the user such that realistic mapping of overall loudness of sound from the acoustic domain to the electrical stimulation domain is maintained.